When the concentration of the inhibitory neurotransmitter lambda-aminobutyric acid (GABA) diminishes below a threshold level in the brain, convulsions can begin. Increasing the GABA concentration terminates the convulsion. Since GABA does not cross the blood-brain barrier, it cannot be used as an anticonvulsant agent. An alternative approach to increase brain GABA levels has been to inactivate the enzyme that degrades GABA, namely, GABA aminotransferase (GABA-AT); for example, the anticonvulsant drug vigabatrin is used in Europe for the treatment of epilepsy. Another approach, which has not yet been exploited, would be to design a class of compounds that activates the enzyme that catalyzes the conversion of glutamic acid into GABA, namely, L-glutamic acid decarboxylase (GAD). Four areas of research on which this proposal will focus are 1) the design of new inactivators of GABA-AT, 2) the elucidation of the active site peptides to which selected inactivators become attached, 3) the determination of the mechanisms of inactivation of various GABA-AT inactivators, and 4) the design and mechanism of action of L-glutamic acid decarboxylase (GAD) activators. The new inactivators of GABA-AT that will be studied include 4-aminotetrahydrofuran-2-carboxylates and the corresponding tetrahydrothiophene and pyrrolidine analogues, beta-lactam sulfones, alpha-substituted aminomethylphenols and 5-aminomethyl-2-hydroxyisoxazole analogues, and 3-aminopropylphosphonic acid analogues. The active site will be probed with radioactively-labeled lambda-vinyl GABA, lambda-ethynyl GABA, and 4-amino-2-fluoro-2-butenoic acid and the structures of peptides to which these compounds become attached will be determined. The mechanisms of inactivation of GABA-AT by 4-amino-4,5-dihydrofuran-2-carboxylate and the corresponding dihydrothiophene analogue, of beta-chloroalanine hydroxamide, of 3-amino-4-fluorobutanoic acid and the corresponding 4,4-difluoro compound, of 4-amino-2-difluoromethyl-2-butenoic acid, and of lambda-fluorovinyl GABA analogues will be investigated. The cause for activation of L-glutamic acid decarboxylase by various compounds will be investigated, the proposed allosteric site peptides will be determined. and new potential GAD activators will be designed and tested.